Paints containing low sheen opacifying pigments obtained by flux calcination of kaolin clay

ABSTRACT

Flux calcined kaolin clay especially useful as a pigment for low sheen paints is obtained by mixing hydrous kaolin with an aqueous solution of alkaline flux, spray drying, pulverizing, calcining and repulverizing.

This application is a divisional of application Ser. No. 09/196,059filed Nov. 19, 1998 U.S. Pat. No. 6,136,086.

BACKGROUND OF THE INVENTION

It is normal practice to produce kaolin pigments by calcination ofpurified fine particle size hydrous kaolin clay. Calcination of kaolinat temperatures up to about 1100° C. cements particles together andproduces products of improved whiteness and opacity. Such pigments arewidely used by the paper, plastics, rubber and paint industries. Aseminal patent is commonly assigned U.S. Pat. No. 3,586,523, Fanselow etal, the disclosure of which is incorporated herein by cross-reference.This patent is directed to producing low abrasion fine particle sizeopacifying calcined kaolin clay, such as the pigments supplied under theregistered trademarks ANSILEX and ANSILEX 93. Such pigments have anaverage particle size of about 0.8 microns. When used in paints, thefine calcined pigments obtained by practice of the Fanselow et al patentalso provide tint strength and high sheen.

For flat paints, the low angle sheen as measured by 85 degree gloss isgenerally less than 10. For better flat paints, the 85 degree sheen is 4or below. To achieve low sheen the particle size of the calcined claysis increased by changing the particle size distribution of the feed suchthat the feed is coarser than used by Fanselow et al. While a sheen of 4is achievable by calcining a coarser feed, the hiding and tint strengthproperties are compromised (reduced). It is extremely difficult tobalance the properties of a paint formulation since 85 degree sheen andopacity/tint strength move in opposite direction to their particle size.Thus, as particle size in the optically efficient range increases,opacification decreases. The following commonly assigned patent, U.S.Pat. No. 4,525,818, Kostanzek, discloses means to produce certain coarsecalcined kaolin clay pigments especially useful as primary extenders inpaint. The calcined clay pigments have an average particle size of about3 to 4 microns.

Practice of our invention utilizes fluxing compounds during calcinationof the kaolin, the compounds being added to hydrous kaolin beforecalcination. Reference is made to U.S. Pat. No. 2,307,239, Rowland,which is a pioneer patent in the field of calcined kaolin pigments. Thispatent broadly discloses addition of various alkali and alkaline earthcompounds to clay before calcination. A preferred compound is sodiumchloride. U.S. Pat. No. 3,853,573, Ferrigno, discloses pigmentarycompositions produced by combining a fluxing agent composed of one or acombination of metal oxides with calcined kaolin, with optional hydrouskaolin, and an inorganic binder. Dry addition of flux is practiced byRowland and Ferrigno; no attempt is made to coarsen the clay in theoptically efficient particle size range. In a thesis, “The Kaolin toMullite Reaction Series,” Wilfred Anthony Martinez, Rutgers University,1979, various “mineralizers” were added to both a fine particle sizekaolin and a relatively coarse particle size hydrous kaolin, primarilyto explore the effect on the crystallinity. Dry addition of mineralizerwas practiced in all experimental work. There is no attempt to controlthe coarsening of kaolin clay during calcination throughout theoptically active size. The phrase “controlled coarsening” as used hereinrefers to increasing the percentage of coarsened particles throughoutthe particle size range of 0.5 to 2 microns.

So-called “flash” or “shock” calcination is used to produce relativelycoarse kaolin derived pigments. Reference is made to U.S. Pat. No.3,021,195, Podschus et al. Special calciners must be used andmulti-stage thermal treatment is used. The rotary calciners or Nicholsfurnaces generally used by the kaolin industry cannot be readilyreconstructed to function as shock calciners. While the calcinedpigments are relatively coarse, average size about 1.4 microns, andsheen is low, the pigments tend to be more yellow than other calcinedclay pigments.

SUMMARY OF THE INVENTION

Our invention overcomes this difficulty by controlled coarsening throughcalcination of hydrous fine size kaolin with controlled low dosages offluxing agents. The controlled coarsening allows the calcined pigmentsto attain unusually low sheen while other important properties such ashiding and tint are not compromised.

The new products can be made with conventional rotary calcination kilnswithout new capital. This does not require use of flash calcinationprocess to produce low-sheen pigments. The experimental products made byour invention have higher whiteness and less yellowness than commercialflash calcined low sheen pigments.

An essential feature of the process is that the fluxing agent must bewater soluble and is added to the hydrous kaolin with mixing in thepresence of water. Dry mixing of flux with clay before calcination, astaught in the prior art, does not result in controlled coarseningthroughout the desired range of 0.5 to 2 microns. Further, dry mixingresults in large amounts of oversize (grit) which may render the productof limited if any commercial use.

DETAILED DESCRIPTION OF THE INVENTION

The fluxing agent may be mixed with kaolin clay in the presence of waterat various points during the processing of hydrous kaolin but ispreferably added to a dispersed slurry of hydrous kaolin in solutionform just prior to spray drying. The spray dried pigment is pulverizedand calcined at temperatures between 500 to 1200° C. but preferablybetween 800 to 1070° C. See Fanselow et al, supra. The calcined productis pulverized before use in formulating paints, paper coating colors,plastics, rubber and other applications. The dosage of fluxing agent andthe type of fluxing agent required are dependent on the hydrous kaolinfeed and its particle size. The upper limit of temperature ofcalcination is dictated by the mullite index. The mullite index measuresthe amount of mullite (3Al₂O₃.SiO₂) formed from calcination.

As taught in Fanselow et al and other patents in the art, kaolin clay isconventionally dispersed before spray drying to provide fluid slurriesof commercially practical solid levels. In typical practice soda ash isadded normally as a part of a dispersant package during dispersion ofkaolin slurries. As in the illustrative examples herein, two dispersantcombinations, SAP and SAC, are generally used. SAP is an 18 to 21%solution of soda ash, partially neutralized polyacrylic acid (C211) andSHMP (sodium hexametaphosphate) at an active ratio of 49/22/29respectively. SAC is an 18 to 20% solution of soda ash and C2111 at anactive ratio of 50/50. Normally the highest level of these dispersantsused is 6 #/T or 0.3% by weight (pH of slurry adjusted to 7.5). Thistranslate to 0.15% soda ash added with SAP and 0.15% soda ash added inthe case of SAC. The highest level encountered in a typical commercialplant is approximately 8 #/T SAP (pH of slurry adjusted to 8.0) whichtranslates to 0.20% soda ash. It is believed that other kaolinmanufacturers also use the same range of soda ash concentrations todisperse their slurries. In the practice of our invention, one of thepreferred fluxes is soda ash. The lowest soda ash level (≧0.30%)employed is at least 50% higher than the highest soda ash level used fordispersing kaolin slurries.

Suitable, preferred and especially preferred feeds for the practice ofthis invention have PSD as follows:

Cumulative Mass Finer (%) Diameter (um) Suitable Preferred MostPreferred 10.0 100 100 100 5.0 100 100 100 2.0 87-100 95-100 96-100 1.070-100 80-99  88-99  0.5 37-95  60-93  70-93  0.3 19-95  35-70  50-70 

At a given dosage of flux, the finer the feed, the greater is the degreeof coarsening across the whole particle size rage. The degree ofcoarsening is defined as the change in % cumulative mass finer betweenthe calcined product and the hydrous kaolin feed at a given diameter(equivalent spherical diameter esu). At the same dosage of flux as thehydrous kaolin feed becomes coarser, the degree of coarsening across thewhole particle size range is less. A broad window for controlledcoarsening is available with a fine feed, the fineness of the feed onlybeing limited by processing capability and economics. If, however, thefeed is too coarse, it becomes increasingly difficult to achievecontrolled coarsening for low sheen, high hiding pigments.

The fluxing agents employed are capable of wide variation that willproduce controlled coarsening of hydrous kaolin on calcination. Thefluxing agents include alkali and alkaline metal ion salts of metaloxides, carbonates or their combinations. Typical metal oxides are boronoxides, silicates, alkali and alkaline earth oxides, germanates,phosphates, alumina, antimony oxide, lead oxide, zinc oxide, arsenicoxide and zirconate. Also included is boric acid. Typical carbonates arealkali and alkaline earth carbonates such as sodium carbonates, sodiumbicarbonates, calcium carbonate and magnesium carbonate. This list is byno means exhaustive. Also included are organic and inorganic non-oxidesalts of alkali or alkaline earth metal capable of forming metal oxideson exposure to air at calcination temperatures including halides,nitrates, acetates, hydroxides, sulfates and organic polyelectrolytessuch as a sodium salt of poly[acrylic acid]. The key criteria is thatthe fluxing agent produces controlled coarsening of hydrous kaolin oncalcination. Preferred fluxing agents are alkali and alkaline earth ofboron oxides, silicates, phosphates, alkali and alkaline earth metalsalts of carbonates and bicarbonates, or their combinations. Especiallypreferred are borax [sodium borate, Na₂O.2 B₂O₃ either in hydrated oranhydrous form], soda ash [Na₂CO₃], sodium silicates with weight ratioof SiO₂:Na₂O of 2.00 to 3.25. They are especially preferred for theirready availability, ease of mixing with hydrous kaolin in slurry formand low dosage level to affect controlled coarsening and its low cost.

The amount of flux added to the hydrous kaolin slurry may vary with theparticle size distribution of the hydrous kaolin feed and thecharacteristics of the fluxing agent including its inherent coarseningability and its alkali or alkaline earth metal oxide equivalent weight.It is recognized that in certain complex flux such as borax, the boronoxide component acts as a network former while the sodium oxidecomponent acts as a network modifier to give a more random networkstructure. Therefore, both components of complex fluxes such as boraxand sodium silicates contribute to coarsening of the particles. For easeof description, the amount of flux is given in terms of sodium oxideweight equivalent. The sodium oxide weight equivalent range is differentfor simple fluxes such as sodium carbonate to that for complex fluxes.The ranges are summarized as follows:

% flux as Na₂O wt equivalent based on dry clay Simple Flux Complex FluxRange 0.02-1.50 0.02-0.75 Preferred 0.20-1.00 0.08-0.55 Most Preferred0.40-0.75 0.16-0.40

In the presence of flux, calcination temperatures range from above 500to 1200 C. and preferably between about 750 to 1100 C., embracing bothmetakaolin and fully calcined conditions. The preferred temperaturerange is chosen to achieve a good balance between pigment PSD,brightness and opacity. Prior art publications disclose that thepresence of certain flux reduces the calcination temperature to arriveat a given mullite content in calcined clay. We found that mullitecontent for fluxed calcined kaolin is not an issue in performance.

The PSD of products preferred and most preferred are:

% Cumulative Mass Finer Than Diameter (um) Preferred Most Preferred 10.075-95 80-95 5.0 55-85 75-88 2.0 45-70 50-70 1.0 30-50 35-45 0.5 2-15 5-15 0.3 0-5 0-5

The most preferred PSD range gives the best balance of low sheen andhigh hiding for the calcined product.

In the practical use of pigments of this invention for paints, it is 15undesirable to have residue levels [retained on a 325 U.S. mesh screen]to be higher than 0.15%(wt.). The residue may appear in the paint filmas grit or give an unsmooth feel. In fact, it is preferred to haveproducts with +325 mesh residue at or below 0.10%(wt.). This iscontrolled by preventing excessive coarsening. The most preferred rangeof PSD for the product normally provide +325 mesh residue at or below0.10%. For calcined products without flux, the amount of mullite(3Al₂O₃.SiO₂) is controlled by avoiding excessive calcination times andtemperature. Our experience with the fluxed product is that even withmullite index normally thought to be high enough to give unacceptableabrasion with paper coating grades of calcined kaolin, in fact gave lowabrasion. Therefore, for fluxed calcined kaolins, the value of mulliteindex is not an issue for performance in paints.

Intended use is in architectural paints in general and in flat interiortrade paints in particular. Flat paints account for over 50% of thetotal volume of trade paint sales. These are high PVC (pigment volumeconcentration) ranging from 55 to 80% formulated above CPVC (criticalPVC). Flat paints as the name suggest have very low gloss. A sheen(measured on 85 degree glossmeter) of 5 or less is highly desirable. Thetop of the line paints customarily have a high TiO2 loading and lowerPVC. They therefore exhibit better hiding and film integrity. Flatpaints also use maximum amount of extenders and calcined kaolin clay isinvariably one of the extenders. The role of the calcined clay is toextend TiO2, improve opacity and tint strength and provide sheencontrol. Products of this invention give very low 85 degree sheen,excellent opacity and tint strength particularly in top of the line flatpaints. A typical premium flat paint formulation is:

For a 55 PVC flat paint using a vinyl acrylate latex resin as binder,the pigment composition is:

Lb./100 gal TiO₂  50-100 Calcined kaolin 180-210

Other potential application area are in exterior flat & interioregg-shell (or satin) paint.

In all examples, pre-dispersed slurries of hydrous kaolin containingdispersant mixtures were used prior to flux addition. In all cases,fluxes were added as solutions prior to incorporation into pre-dispersedslurries.

The following test procedures were used in the illustrative examples:

GEB—TAPPI Method T646 om-86 (brightness of clay and other mineralpigments)

PSD (Particle Size Distribution)—Measured with Sedigraph usingMicromeritics SEDIGRAPH 5100; reported on a weight bases.

Contrast Ratios—measures hiding power of paints by reflectometry—ASTMD2805-88

Reflectance—ASTM D2805-88

Whiteness—ASTM E313-73

Yellowness—ASTM E313-73

Sheen—measures near-grazing shininess or specular gloss at 85°geometry—ASTM D523-80

Tint Strength Y—standard method for relative tint strength of whitepigments by reflectance measurements—ASTM D2745-80

Gardner Coleman Oil Absorption Test is based on ASTM D-1483-84

Mullite Index is determined by an Engelhard Standard Lab Test Method MGA0990.1. The automated powder X-Ray diffractometer is used to determinethe integrated peak intensities of 2 Mullite reflections (121 and 331)for the calcined kaolin sample, a 100% reference Mullite and one workingstandard. The method generates a number designated as the Mullite Index,which is the ratio of the average integrated intensity of thereflections for a sample, to the corresponding reflections for the setof working standards.

EXAMPLE 1

Several hydrous kaolin feeds of different average particle size andwithout added flux were calcined at 1066° C. The particle size of thefeed and calcined product are given in Table 1. Data in Table 1 showthat on calcination, the average particle size increased with feedparticle size. The pigments were formulated into 55 PVC latex flatpaints using a vinyl acrylic latex resin as binder. The pigment formulaused in units of lb/100 gal consisted of 100 lb. of TiO2 and 180 lb. ofcalcined kaolin clay. Total solids were 35.64% by weight and 22.81 byvolume.

When formulated in 55 PVC latex flat paints, A and B pigments have highhiding (high contrast ratio) and tint strength but very high sheen. Notethat A and B are representative of pigments obtained by practicing theteachings of Fanselow et al. These attributes disqualify A and Bpigments from being used in flat paints. The coarser C pigment at 1.4micron average particle size gave 5.9 sheen and sufficient hiding andtint to qualify it for use in flat paints. For premium flat paints,however, sheen values of 4.0 or below is desired.

TABLE 1 Typical Paint of Conventional Calcined Kaolin Clays in 55 PVCLatex Flat Paint Pigment A B C Ave Particle Size of feed in um 0.3 0.40.7 Ave Particle Size of product in um 0.8 0.9 1.4 As 55 PVC latex FlatPaint* Properties Contrast Ratio 1.5 mils 95.9 96.02 91.5 Contrast Ratio3.0 mils 98.8 98.5 96.4 Reflectance 94.8 95.0 92.2 Whiteness 81.3 84.076.6 Yellowness 3.57 2.88 4.24 Sheen 85 degree 22.7 13.4 5.9 TintStrength Y 56.3 55.4 47.2 *Pigment Formula in lb/100 gal:100 TiO2, 180calcined kaolin clay

EXAMPLE 2

In accordance with the present invention, a filter cake of hydrouskaolin with an average particle size of 0.2 micron was dispersed andsufficient aqueous solution of 2.0% sodium tetraborate decahydrate(borax) added to provide a 1.0% dosage on kaolin solids. The slurry wasmixed thoroughly for an additional 15 minutes. The pH of the slurry was8.8. The slurry was spray dried and pulverized in a Mikro Mill (fromPulverization Machinery Co., of Summit, N.J.). The pulverized materialwas calcined in a Thermolyne muffler furnace at 815° C. The product waspulverized in conventional manner. The sample was identified as D. Aseparate sample, identified as E, was calcined at 1066° C. andpulverized. The pigments were formulated into 55 PVC latex flat paintsusing a vinyl acrylic latex resin as binder. The pigment formula used inunits of lb/100 gal consisted of 50 lb. of TiO2 and 210 lb. of calcinedkaolin clay. Total solids were 36.86% by weight and 22.78 by volume.

The properties of pigments D and E are compared with C together withflat paint performance properties in Table 2. Also compared is acommercial double calcined pigment supplied under the registeredtrademark OPTIWHITE (flash calcination followed by conventionalcalcination) from Burgess Pigment.

The borax containing pigments D and E are finer in average particle sizethan C, but produced dramatically lower sheen, higher hiding and tintstrength than C. Pigments D and E are considered excellent pigments forpremium flat paints. The commercial shock calcined kaolin showedslightly higher sheen, lower hiding and tint strength than either D andE. Pigment E gave higher whiteness and less yellowness than OPTIWHITEpigment.

TABLE 2 Comparative Properties and Flat Paint Performance of Borax FluxCalcined Kaolin OPTI- Pigment C D E WHITE % borax 0 1.0 1.0 0Calcination Temperature 1066 C 815 C 1066 C GEB 90-92 91.0 92.9 91 AveParticle Size of Feed in um 0.7 0.2 0.2 Ave Particle Size of Product inum 1.4 .7 1.0 1.4 % at 10 um 98.1 88.6 85.0 95.9 % at 5 um 89.0 73.670.0 87.7 % at 2 um 61.7 61.6 57.6 62.1 % at 1 um 38.2 56.0 48.8 34.8 %at 0.5 um 10.5 20.0 13.8 5.6 As 55 PVC latex Flat Paint* PropertiesContrast Ratio 1.5 mils 89.5 92.7 91.2 90.1 Contrast Ratio 3.0 mils 96.397.4 97.1 96.1 Reflectance 91.8 95.2 95.0 94.3 Whiteness 79.0 73.4 76.372.7 Yellowness 3.48 4.71 3.92 4.73 Sheen 85 degree 5.1 2.5 2.8 3.1 TintStrength Y 47.9 56.9 55.8 53.1 *Pigment in lb/100 gal:50 TiO2, 210calcined kaolin clay

EXAMPLE 3

A hydrous feed slurry used for making ANSILEX 93 hydrous kaolin wasmixed thoroughly with 0.75% of sodium carbonate (soda ash). The slurrywas spray dried and pulverized in a Mikro Mill. The pulverized materialwas calcined in a Thernolyne muffler furnace at 1066° C. The product waspulverized and the sample identified as F. A separate sample identifiedas G was prepared in the exact manner as F except that the feed slurrywas mixed with 1.0% soda ash before spray drying. The physicalproperties and flat paint performance of pigments F and G are comparedwith OPTIWHITE pigment in Table 3.

The soda ash modified pigments F and G showed at least equivalentproperties compared to that of OPTIWHITE. An advantage seen issignificantly lower 85 degree sheen than OPTIWHITE to give greaterflatness in paint.

TABLE 3 Properties and Flat Paint Performance of Soda-Ash Flux CalcinedKaolin Pigment F G OPTIWHITE % soda ash (Na2CO3) 0.75 1.0 0 CalcinationTemperature in C 1066 1066 GEE 91.7 91.4 91 Ave Particle Size of Feed inum 0.25 0.25 Ave Particle Size of Product in um 1.5 1.8 1.4 % at 10 um87.0 83.3 95.9 % at 5 um 75.7 70.2 87.7 % at 2 um 57.5 52.6 62.1 % at 1um 33.8 30.3 34.8 % at 0.5 um 6.6 6.1 5.6 As 55 PVC latex Flat Paint*Properties Contrast Ratio 1.5 mils 90.4 90.2 89.8 Contrast Ratio 3.0mils 96.6 96.3 96.2 Reflectance 89.8 89.4 89.4 Whiteness 73.3 72.4 73.1Yellowness 4.58 4.74 4.57 Sheen 85 degree 1.5 1.1 3.0 Tint StrengLh Y51.7 5O.47 51.5 *Pigment inlIb/100 gal:50 T102, 210 calcined kaolin clay

EXAMPLE 4

In accordance with a presently preferred embodiment of our invention, anANSILEX 93 hydrous feed slurry was mixed thoroughly with 1.0% by weightof sodium silicate (based on clay solids) with a modulus of 2.88. Theslurry was spray dried and pulverized in a Mikro Mill. The pulverizedmaterial was calcined in a Thermolyne muffler furnace at 1066° C. Theproduct was pulverized and the sample identified as H. A separate sampleidentified as I was prepared in the exact manner as H except that thefeed slurry was mixed with 1.25% sodium silicate before spray drying.The physical properties and flat paint performance of pigments H and Iare compared with OPTIWHITE pigment in Table 4. The paint formulationswere identical to that described in Example 2.

The sodium silicate modified pigments H and I showed at least equivalentproperties compared to that of OPTIWHITE pigment. An advantage seen inthat H gave significantly lower 85 degree sheen than OPTIWHITE pigment.

TABLE 4 Properties and Flat Paint Performance of Sodium Silicate FluxCalcined Kaolin Pigment H I OPTIWHITE % Sodium Silicate (2.88 modulus)1.0 1.25 0 Calcination Temperature in C. 1066 1066 GEB 90.9 91.0 91 AveParticle Size of Feed in um 0.25 0.25 Ave Particle Size of Product in um1.4 % at 2 um 54.9 59.2 62.1 % at 1 um 29.5 35.5 34.8 % at 0.5 um 5.26.5 5.6 As 55 PVC latex Flat Paint* Properties Contrast Ratio 1.5 mils91.3 91.2 90.8 Contrast Ratio 3.0 mils 96.7 96.5 96.7 Reflectance 89.189.3 88.9 Whiteness 72.5 72.4 73.0 Yellowness 4.67 4.74 4.47 Sheen 85degree 2.3 3.1 3.1 Tint Strength Y 44.4 44.2 44.2 *Pigment in lb/100gal: 50 TiO2, 210 calcined kaolin clay

EXAMPLE 5

This example shows that the controlled coarsening of feed useful toproduce ANSILEX 93 with calcined kaolin pigment soda ash flux resultedin lower oil absorption that is similar to that produced by the flashcalcined OPTIWHITE pigment. The lower oil absorption is a desiredproperty with benefits in providing higher loading of extender andimproved scrub resistance of the paint film.

Oil Absorption Data Comparison: Gardner Coleman Method

Oil Absorption Data Comparison: Gardner Coleman Method 1.0% Soda AshANSILEX 93 flux ANSILEX 93 OPTIWHITE Oil Absorption 105-120 87 85 APS um0.78 1.32 1.4

EXAMPLE 6

The results of the following tests indicate that wet processing (usingsoda ash and sodium chloride) followed by spray drying of ANSILEX 93feed produces benefits not obtained by dry blending. The desired coarserbut balanced PSD products are obtained using the wet processing method.The dry blend method gave significantly higher residue (retained on a325 mesh screen) that was about 5 to 19 times higher than the wetprocessing method.

For these samples calciner feed and spray dryer feed was recovered at acommercial plant. To simulate prior art, the dry soda ash was added(0.8%, 1.2% and 1.6%) and mixed with hydrous kaolin in a roller mill for1 hour. Then it was ball milled for 15 minutes. PSD analyses wereperformed, before and after ball milling. NaCl (dry) was added to onesample in amount of 3% by weight of the kaolin, following which it waspulverized, using the same procedures employed with soda ash. Theparticle size distribution (PSD) of the dry blended kiln feed samplesare given in Table 5. Within experimental error for measuring PSD usingSEDIGRAPH analysis, no change was seen in the PSD resulting from dryblends of soda ash (SA) to ANSILEX 93 feed. This was true whether theblend was simply roller milled or subsequently ball milled. For purposesof comparison the same amounts of soda ash and NaCl were added topredispersed slurries and spray dried. These were then pulverized andall were calcined at 1950° F. and post pulverized.

TABLE 5 Properties of Dry blended Kiln Feed Samples Sample Ball mill 2um 1 um .5 um .3 um Med. um A93 NO 95.8 88.0 71.4 49.0 0.31 A93 YES 96.888.6 71.9 49.7 0.30  .8% SA NO 96.3 88.5 72.1 49.6 0.30  .8% SA YES 95.988.0 71.7 49.0 0.31 1.2% SA NO 96.4 89.1 71.6 48.9 0.31 1.2% SA YES 96.188.1 70.8 48.5 0.31 1.6% SA NO 96.4 88.5 70.9 48.3 0.31 1.6% SA YES 96.388.7 70.4 48.1 0.31

TABLE 6 Properties of Flux Calcined Kaolins Derived From Dry Blended andSlurried Feeds Dry/ Test slurry hr L A B YI 2 um 1 um .5 um .3 um Med.Res. As is Slurry 92.4 97.66 −0.65 2.95 4.44 81.8 58.3 11.9 2.8 0.880.015 As is Dry 92.2 97.66 −0.60 2.85 4.31 89.7 69.7 19.7 4.1 0.74 0.032 .8% SA Slurry 91.8 97.51 −0.68 2.90 4.39 74.5 47.3 9.4 2.3 1.05 0.037 .8% SA Dry 91.7 97.39 −0.54 2.77 4.19 87.7 68.4 19.8 4.1 0.75 0.170 1.2SA Slurry 91.7 97.54 −0.70 2.91 4.39 68.3 39.8 6.1 1.3 1.21 0.037 1.2 SADry 91.7 97.37 −0.62 2.75 4.16 85.1 66.3 19.6 4.4 0.76 0.307 1.6 SASlurry 91.5 97.44 −0.69 2.96 4.47 67.2 38.7 7.0 2.6 1.24 0.018 1.6 SADry 91.5 97.33 −0.62 2.71 4.10 82.4 64.7 19.1 3.7 0.77 0.340 3 NaClSIurry 92.6 97.74 −0.70 2.74 4.14 72.4 36.2 5.3 2.O 1.24 0.04 3 NaCl Dry92.8 97.73 −0.58 2.56 3.86 80.5 44.9 7.3 2.I 1.08 0.256 Br = GEB,pigment brightness TAPPI T646-om-86 L = Hunter L* A = Hunter A* B =Hunter B* YI = pigment yellowness index* Res = +325 mesh residue in %*ASTM - D2244-79, also, Color Science, G. Wyszecki/W.S. Stiles, Wiley1967

The properties of flux calcined kaolins derived from dry blended andslurried feeds are summarized in Table 6. In all cases, the wetprocessing or slurry route for incorporating the flux to the pigmentgave more extensive coarsening but significantly less residue. Thisindicates that desired coarsening is achieved more advantageously by thewet processing or pre-slurrying the flux with the hydrous kaolin pigmentthan by dry blending.

We claim:
 1. A low sheen paint composition comprising flux calcinedkaolin clay that is 75 to 95% by weight finer than 10 microns, 55-85% byweight finer than 5 microns, 45-70% by weight finer than 2 microns,30-50% by weight finer than 1 micron and 2-15% by weight finer than 0.5micron, and has an average particle size in the range 1.0 to 2.5microns.
 2. The low sheen paint composition of claim 1 wherein the fluxis sodium carbonate.
 3. The low sheen paint composition of claim 1wherein the flux is sodium silicate.